Tensions start to rise between Carol and Tyreese when Michonne is introduced, and Carol begins to fear Tyreese will be attracted to her.
Carol tries to ignore Tyreese and Michonne's friendship for some time and simply just brush it off as nothing, until she witnesses Michonne performing oral sex on Tyreese in the prison gymnasium.
It was then that she officially split up with Tyreese, demanding that he gather his things and move out the following day.
Soon after the break-up however, her mentality came into question, due to Tyreese's betrayal and the global apocalypse in general.
She is the mother of Sophia and a member of the Atlanta band.
It's been heavily implied that she faced little satisfaction throughout her many years of marriage and only stayed with him because she both needed as much help as she could get taking care of Sophia and also because of her needy tendencies.
Lori was also who she relied upon the most for support whenever it was needed.
She and Sophia managed to survive the deadly attack at the campsite, nearly being attacked, but, saved at the last second by Glenn.
Once the apocalypse broke out, her husband was traumatized, forced to see his parents die in front of him and supposedly become zombies.
After this event, he was driven into a deep depression and Carol's relationship with him became increasingly strained.